Uterine contractions during labour can restrict maternal uterine and/or fetal umbilical blood flow compromising fetal oxygenation and leading to fetal hypoxia/acidosis. Fetal monitors of various types are widely used in the obstetrics field.
Fetal heart rate (FHR) monitoring is widely used during labour and FHR decelerations predict hypoxic change. Numerous studies using electro-cardiogram (ECG) and FHR have been published. Intrapartum fetal ECG readings are obtained through the scalp electrodes. A drawback of the various types of fetal monitors currently used in obstetrics is that they provide for poor positive predictive value for fetal acidosis. After many caesarian deliveries performed on the basis of FHR information using these conventional techniques, it has been found that the fetus was not really in critical distress.
Monitoring of oxygen saturation can allow direct assessment of both fetal oxygen status and fetal tissue perfusion. Pulse oximetry, a subclass of the general field of oximetry, uses changes in arterial blood volume through a heart beat cycle to internally calibrate oxygen saturation measurements. However, knowledge of fetal oxygen saturation does not appear to lower the rate of unnecessary caesarean sections or improve infant health (Bloom et al., New England Volume 355:2195-2202).